This research is proposed to improve understanding of how hybridization between genetically distant organisms contributes to the evolution of novel phenotypes and how environmental pressures shape the resultant phenotypic diversity. The specific aims are: 1) to determine structural and content diversity of specific classes of terpenoid metabolites in plant hybrid species complexes, with comparison of naturally- existing and experimentally-created hybrids as well as measurement of variation across development and in response to stress stimuli; 2) to determine how variation in transcriptional response and functional variation in structure of specific biosynthetic enzymes impacts the metabolic output of these natural and artificial hybrid species complexes; and 3) to identify the genetic bases of structural variation in terpenoid metabolites. Biochemical analyses of terpene structures will be conducted on parental and hybrid species using modifications of existing analytical protocols for HPLC-MS and NMR. Genetic loci encoding enzymes responsible for early stages of terpenoid biosynthesis will be identified from existing literature or via homology to known enzymes. Variation in DNA sequence and mRNA transcript accumulation for these specific enzymes will be measured via standard sequencing protocols and quantitative PCR. Additional candidate loci controlling structural variation will be identified using structured mapping populations and homology to terpenoid modification loci identified in model plant species, with activity of these candidate enzymes evaluated via heterologous expression in yeast and bacterial systems. How genomic contributions from diverse parents interact to create unique phenotypes is a biological question of basic importance to understanding the genetic bases and evolution of biological traits in sexually-reproducing species, including humans. Plant systems are particularly useful for such studies as interspecific crosses are both genetically feasible and ethically permissible. The metabolic phenotypes to be explored are additionally relevant to public health due to the allergenicity and potential therapeutic uses of terpenoid metabolites, and the potential utility of these studies in metabolic engineering.